Method for making knock-outs in electrical boxes formed of plastic material

ABSTRACT

Knock-outs are formed in electrical fixtures, such as connector boxes made of plastic sheet material by punching the knock-outs from plastic sheet or blanks prior to shaping into the fixture or by shaping the fixture and then punching out the knock-outs. By resiliently supporting the material surrounding the knock-out area on the punch side and resilient biasing a knock-out stripper against the surface of the knock-out opposite that contacted by the punch, knock-outs can be punched out and replaced in the material in a single operation if the opposite biasing forces of the support and knock-out stripper are properly correlated.

FIP7904 XR 397359653 United States Patent r [11] 3,735,653 Powell 1 May29, 1973 [54] METHOD FOR MAKING KNOCK-OUTS FOREIGN PATENTS ORAPPLICATIONS IN ELECTRICAL BOXES FORMED OF PLASTIC MATERIAL [75]Inventor: James C. Powell, Elkhart, Ind.

672,406 5/1952 Great Britain ..83/25 Primary ExaminerFrank T. Yost [73]Assignee: All-Steel Equipment Inc., Aurora, AtmmeyMann,BTWn& McwiniamsIll. 1

[22] Filed: Dec. 7, 1970 I [57] ABSTRACT [21] A l. N 95,922 Knock-outsare formed in electrical fixtures, such as connector boxes made ofplastic sheet material by Related Applkation Dam punching the knock-outsfrom plastic sheet or blanks [62] Division of Ser. No. 783,584, Dec. 13,1968, Pat. No. prior to Shaping into fixmm by Shaping the 3,580,122 tureand then punching out the knock-outs. By resiliently supporting thematerial surrounding the 52 us. Cl. ..83/l, 83/25, 83/108, area thePunch Side and resilient biasing 83/695 21 knock-out stripper againstthe surface of the knock- 51 Int. Cl. ..B26d 7/18 that contacted by thePunch [58] Field of Search ..s3/25, 108, 1, 103, can be Punched andreplaced in mater'al a 83/685 686 695 single operation if the oppositebiasing forces of the support and knock-out stripper are properly corre-[56] I References Cited lated- UNITED STATES PATENTS I 3 Claims, 5Drawing Figures 3,383,065 5/[968 Bergeron et alt ..83/l08 X BRIEFSUMMARY OF THE INVENTION This invention is directed to plastic electricfixtures, such as electrical boxes, containing knock-outs and apparatusand method for making such knock-outs.

In fabricating electrical boxes and other fixtures it is necessary toform knock-outs which can be easily removed from the box for the purposeof permitting electrical wires to pass therethrough and for fasteningthe ends of the conduits through which the wires pass.

It has been discovered that knock-outs can be formed in the sheet (fromwhich the box is formed) in a continuous manner prior to cutting the boxblanks from the sheet by supporting the sheet area surrounding the punchagainst a spring-mounted stripper plate by means of springs whichnormally hold the plate in a predetermined position but which permit theplate to be depressed during the punching operation. One or moreknock-out punches are fixedly mounted so that they extend through holesin the plate with their end surfaces coplanar with the surface of thestripper plate when the stripper plate is in normal position. The diecavity contains a knock-out stripper element which is spring-biased inthe direction of the knock-out punches and is slideably mounted in thedie cavity. When the die is actuated on its work stroke, thespring-biased knockout stripper is biased against the plastic sheet. Theplastic sheet is held tightly between the stripper plate and the die,causing the knock-out to be punched out of the sheet and held betweenthe knock-out punch and the knockout stripper. On the release stroke ofthe die the springs force the stripper plate and sheet upwardly. Theopposing biasing force of the knock-out stripper and stripper platesprings is sufficient to reinsert the knockout in the hole from which itwas punched in substantially coplanar relationship with the sheet,whereupon the die engages the knock-out stripper causing it to move inunison with the die. The sheetis then free to be advanced to the nextstation.

When the article is preformed before the knock-outs are punched theoperation can be performed by placing the article on a fixed die shapedso as to enable the shaped article to fit snugly thereon, and theknock-outs are punched with a moving punch. The articles can be placedon and removed from the die by hand or by a suitable mechanism.Otherwise the essential operation is the same as that described inconnection with the punching of sheet material.

It is an object of the invention to provide apparatus for formingpunched knock-outs in plastic sheet. It is another object of theinvention to provide an apparatus for forming knock-outs in preformedplastic articles intended for use as electrical fixtures.

It is still another object of the invention to provide a method forforming punched knock-outs in plastic sheet material or preformedplastic articles.

Still another object of the invention is to provide plastic bodies withpunched knock-outs that can be readily removed.

SHORT DESCRIPTION OF THE DRAWINGS FIG. 1 is a vertical cross-sectionthrough the center of the apparatus for punching knock-outs in plasticsheet material in accordance with the invention;

FIG. 2 is a two position vertical cross-section through the center ofapparatus for punching knock-outs in formed plastic articles.

FIG. 3 is a fragmentary perspective view of a punch;

FIG. 4 is a fragmentary perspective view of a die; and

FIG. 5 is a fragmentary perspective view of an electrical box showing aknock-out formed in accordance with the invention.

DETAILED DESCRIPTION OF THE INVENTION Referring to FIG. 1, the numeral 1represents a die shoe which is solidly mounted to the floor. The dieshoe has recesses 3 and 5 to receive helical coil springs 7 and 9respectively.

Removably mounted on the die shoe 1 is a punch holder 11 formed withholes 13 and 15 to allow the springs 7 and 9 to pass therethrough. Tops17 and 19 of the springs 7 and 9, respectively, extend above the uppersurface 21 of the punch holder 11 so that the normal distance betweenpunch holder 11 and stripper plate 12 is somewhat greater than thethickness of the plastic sheet 23 which is to be fed into the device toinsure the forming stroke length that is desired.

Mounted in the punch holder 11 are punches 25 and 27 formed withenlarged bottoms 29 and 31 to provide shoulders for abutting against thesurface 33 of the recess 35 in the bottom of the punch holder 11.Punches 25 and 27 pass through aligned holes in the punch holder 11 andstripper plate 12. Stripper plate 12 is mounted on coil springs Hand 19with its upper surface 39 coplanar with the upper surfaces of punches 25and 27 when the plate is in its normal position. As shown in the drawing(FIG. 1), the plate 12 is in depressed position as a result of theknock-out die 41 being at the end of its power stroke. A block 43 fitsin a recess in the upper surface of die shoe 1 to provide a bearingsurface for the knock-out punches 25 and 27.

Immediately above stripper plate 12 is the knock-out die 41 withcavities 44 and 45 in alignment with the knock-out punches 25 and 27.The die is preferably formed with a small groove 46 (see FIG. 4)extending along each die cavity and each punch is formed with a somewhatlarger groove 47 (see FIG. 3) extending inwardly from the outer wall ofthe punch in order to allow a small tab 206 (FIG. 5) to remain holdingthe knock-out to the sheet. Within the die cavities are mountedknock-out strippers 40 and 50 which are snugly and slidably mounted. Theupper portions of the die cavities are enlarged at 51 and 52 to receivethe enlarged portions 53 and 55 of the knock-out strippers. The heads 57and 59 of the knock-out'strippers are further enlarged to form shouldersto abut against release plate 61 mounted on the top of the die 41. Therelease plate 61 is formed with openings to accommodate the enlargedportions 53 and 55 of the knock-out strippers.

The enlarged head elements 57 and 59 are adapted to contact releaseplate 61 when the bottom surfaces of the knock-out strippers 40 and 50are substantially coplanar with the bottom surface 62 of die 41.

Mounted above release plate 61 is a spacer 63, the

with recesses 67 and 69 in which to accommodate coil springs 71 and 73.The upper ends of the coil springs 71 and 73 abut the top of the element65 and the lower ends of the springs abut the top surface of theknockout strippers 49 and 50 and bias them in the direction of theknock-out punches 25 and 27. Springs 71 and 73 have sufficientcompressive strength to resist the tendency of knock-out strippers 49and 50 to move upwardly until engaged by release plate 61. The actuatorelement 65 is caused to reciprocate by a power means, not shown, over alimited stroke longer than the thickness of the plastic sheet 23. Thespacer element 63 is formed with a cavity 75 sufficiently large toaccommodate the enlarged heads 57 and 59 of the knock-out strippers 40and 50 and permit the spacer 63 to move both downwardly and upwardlywithout abutting the heads 57 and 59.

The operation of the device is as follows: a roll or strip of plasticsheet material 23 is fed by an intermittent feeding means, not shown,over the stripper plate 12 between the punches 25 and 27 and the die 41.While the sheet 23 is in a stationary position, the actuating mechanismfor the actuator 65 depresses the die 41, causing the punches 25 and 27to punch circular knock-outs 77 and 79 from the sheet 23. Since thepunches 25 and 27 are stationary, the sheet moves downwardly with thedie 41 and stripper plate 12 with the knock-outs 77 and 79 being grippedbetween the knock-out punches and corresponding knock-out strippers. Onits release or upward stroke, as the die moves upwardly, the releaseplate 61 abuts the shoulders formed by the enlarged heads 57 and 59 ofthe knockout strippers but only after the sheet 23 gripped between thestripper plate and the die rises to its normal position under the biasof the springs 7 and 9 so that the knock-outs are reinserted in theholes from which they were punched. The release plate 61 engages theknockout strippers and releases the knock-outs when the knock-outs areinserted flush with the surface of the sheet 23 by reason of the factthat the spacing between the release plate 61 and the lower surfaces ofthe heads 57 and 59 at the end of the former stroke is substantially thesame as the thickness of the sheet.

When the die 41 is lifted free of the sheet 23, the feeder automaticallyfeeds the sheet to the next station and the process is repeated.

It will be evident that any desirably number of knockouts can be punchedsimultaneously in the sheet. Although I have only shown two punches, thenumber may be equal to the number required to punch all the knock-outsout of a section of the sheet necessary to form a box. It will also beobvious that the stripper plate may be supported by a number of springsgreater than two.

After the knock-outs are punched and the sheet released as justdescribed, the sheet continues to advance and may then be cut into theblanks of the desired shape and size containing the knock-outs ready forcold-forming.

Referring to FIG. 2, the numeral 100 indicates a shoe having side walls102 and 104 mounted thereon. A hardened steel plate 106 is fastened toeach of the walls 102 and 104.

Spaced inwardly from the walls 102 and 104 are punch holders 108 and 110. The punch holders are fastened to the shoe 100. Mounted in the punchholders 108 and 110 are punches 112 and 114 respectively.

The punches are formed with elongated grooves 116 and 118 similar tothose shown in FIG. 3. Punches 112 and 114 are snugly and slidablymounted in punch holders 108 and respectively.

Punch 112 is fastened to a spacer plate 120 and to an actuator 122 bymeans of bolt 124 passing through a central hole in the actuator andplate and threaded into a threaded recess in the punch 112. Actuator 122is formed with cam surface 125. Punch 114 is similarly fastened tospacer 126 and actuator 128 by means of bolt 130 passing through centralopenings in the spacer plate 126 and actuator 128 and threaded into athreaded recess in punch 114. Actuator 128 is formed with cam surface132. Punch holder 108 is provided with hardened steel plates 134 and 136between which the spacer plate 120 and the actuator 122 are adapted toslide. Holder 110 is similarly equipped with hardened steel plates 138and 140 between which the spacer plate 126 and actuator 128 are adaptedto slide. Punch holder 108 is provided with two or more equally spacedpassageways 142 through each of which is adapted to pass a coiled spring144, the inner end of which is seated in a recess 145 in spring retainer146 and the outer end of which is seated in a recess in stripper plate148. Stripper plate 148 is slidably mounted on the punch. Springs 144normally hold plate 148 in a position such that its surface is coplanarwith the nose surface of punch 112. Similarly, punch holder 110 isprovided with two or more passageways through each of which passes acoil spring, the inner end of which is retained in spring retainer 150and the outer end of which is retained in stripper plate 152.

Each punch holder is also provided with two or more equally spacedrecesses 154 between recesses 145 in which seat one end of coil springs156. The other end of springs 156 seat in recesses 157 in springretainers 146 and 150. The force of springs 156 is sufficient to returnthe punch to its normal position shown on the left hand side of thedrawing.

Mounted on the shoe 100 between the two punches is die block 158 havingdie cavities 160 and 162 aligned with punches 112 and 114 respectively.The end portion of each die cavity is counter-bored and there isinserted therein a hardened steel inserts or rings 164 and 166, againstwhich knock-out strippers 168 and 170, respectively, slide. The insertsor rings 164 and 166 are formed with elongated grooves 172 and 174,respectively, aligned with grooves 116 and 118 in punches 112 and 114 inorder to allow the knock-out punch to retain a tab to fasten it to thearticle in which it is formed.

Mounted in the die cavities 106 and 162 are knockout strippers 168 and170 having cam surfaces 176 and 178. The strippers 168 and 170 arebiased outwardly by biasing element 180 having conical cam surface 182which coacts with the cam surfaces 176 and 178. Biasing element 180 isforceably held against the knock-out strippers 176 and 178 by means of acoil spring 183 or other resilient force. The lower end of the biasingmeans element 180 is mounted in guide 184 which is fastened to shoe 100by element of suitable bolts 186 threaded into the shoe. In addition toacting as a retaining means for spring 183, shoulder 188 limits theupward travel of biasing element 180.

Mounted on power actuated reciprocating beam 190 are cams 192 and 194 inalignment with the space between the wall 102 and holder 108 and thewall 104 and the holder 110, respectively. Came 192 and 194 are formedwith cam surfaces 196 and 198 which are adapted to engage the camsurfaces 125 and 132, respectively, during the power stroke of the beam.The width of the cams 192 and 194 is such that when they enter thespaces 200 and 202, respectively, they force the punches toward the dieblock for a distance sufficient to punch a knock-out from the articlemounted on the die as shown on the right hand side of the drawmg.

The drawing is split into two parts; the right half showing theapparatus in position when a knock-out has been punched and the lefthalf in position of release.

The operation of the apparatus is as follows. An electrical box or otherelectrical fixture made of plastic sheet material is mounted on the dieblock 158 while the punches are in release position. As the beam 190descends the cams 192 and 194 enter the spaces 200 and 202,respectively, forcing the punches and the stripper plates against theouter surface of the article to be punched. As the punch moves to theleft, as shown on the right hand side of the drawing, a knock-out ispunched but remains fastened to the article by means of the tab 206.Knock-out stripper 170 is forced to the left as the knock-out is beingformed but by reason of the fact that it is biased toward the punch, theknockout is held tightly between the knock-out stripper and the punch.

During the release stroke, the stripper plate as shown on the right sideof the drawing remains in contact with the face of the article in whichthe knockout is formed until the knock-out stripper 170 forces theknock-out back into the hole from which it was punched and intosubstantially coplanar relation with the surface of the article as shownon the left side of the drawing. The stripper plate 152 will remainpressed against the surface of the article until the cam 194 during itsrelease stroke allows punch 114 to return to a position out of contactwith the knock-out. As the springs 156 force the punch, spacer andactuator rearward to fully release position as shown on the left side ofthe drawing, the stripper plate is released from contact with thearticle. The apparatus is then ready to have the punchedout articleremoved and another blank inserted on the die block.

The force of the springs 144 which bias the stripper plates against thesurface or area surrounding the knock-out and the opposing force of theresilient means 183 forcing the knock-out stripper against the knock-outare sufficient to cooperate to force the knock-out back into the holefrom which it was punched, during the release stroke of the punch, sothat at the end of the operation the knock-out is replaced or reinsertedin the material in substantially coplanar relationship therewith andheld in placeby a small tab as shown in FIG. 5. The knock-out can thenbe removed from the article in either direction simply by pushing it outwith the thumb or other finger and breaking the tab by bending theknock-out. The tab arrangement provided thus permits the knock-out to bebroken off outside the circumference of the hole or opening formed bythe knock-out.

Although the invention is applicable to various types of plasticmaterial and articles which have the required ductility and resiliency,it is particularly applicable to the formation of knock-outs in sheetand articles made from acrylonitrile-butadiene-styrene copolymersgenerally known as ABS, such as those sold by Rohm and Haas Companyunder the name Kydex and alloys of ABS and PVC (polyvinyl chloride) soldunder the names Cycovin KR and Royalite 20 by Marbon Chemical Companyand Uniroyal, Inc. respectively.

I claim: 1. The method of forming, in solid plastic sheet materialemployed in electrical boxes, knock-outs that are to serve as theknock-outs for the box, said method comprising placing the sheetmaterial between a die member and a knock-out punch member,

moving one of said members relative to the other memberand against oneside of said sheet to punch a knock-out from said sheet while at thesame time forming outside the periphery of the knock-out a tab in saidsheet connecting the knock-out to the sheet, and resiliently supportingthe knock-out from the other side of the sheet by means of a knock-outstripper resiliently biased toward the punch member to limitdisplacement of the knockout laterally of the sheet to a distanceapproximating the thickness of the sheet for precluding severing of thetab while forming a knock-out opening in said sheet,

resiliently supporting the sheet portion surrounding said knock-outopening during the release stroke of said one member by means of astripper plate applied to the other side of the sheet,

and applying sufficient resilient force to the knockout stripper and tothe stripper plate during the release stroke of said member to returnthe knockout to said knock-out opening and in substantial coplanarrelation with said sheet portion.

2. The method set forth in claim 1 wherein:

the die member is said one member and the punch member is fixed againstmovement relative to said one member.

3. The method set forth in claim 1 wherein:

the punch member is said one member and the die member is fixed againstmovement relative to said one member.

1. The method of forming, in solid plastic sheet material employed inelectrical boxes, knock-outs that are to serve as the knock-outs for thebox, said method comprising placing the sheet material between a diemember and a knock-out punch member, moving one of said members relativeto the other member and against one side of said sheet to punch aknock-out from said sheet while at the same time forming outside theperiphery of the knock-out a tab in said sheet connecting the knock-outto the sheet, and resiliently supporting the knock-out from the otherside of the sheet by means of a knock-out stripper resiliently biasedtoward the punch member to limit displacement of the knock-out laterallyof the sheet to a distance approximating the thickness of the sheet forprecluding severing of the tab while forming a knock-out opening in saidsheet, resiliently supporting the sheet portion surrounding saidknockout opening during the release stroke of said one member by meansof a stripper plate applied to the other side of the sheet, and applyingsufficient resilient force to the knock-out stripper and to the stripperplate during the release stroke of said member to return the knock-outto said knock-out opening and in substantial coplanar relation with saidsheet portion.
 2. The method set forth in claim 1 wherein: the diemember is said one member and the punch member is fixed against movementrelative to said one member.
 3. The method set forth in claim 1 wherein:the punch member is said one member and the die member is fixed againstmovement relative to said one member.